At present, most of the thermal power plants in China utilize coal-fired units. Due to the increasingly stringent requirements on air pollution control from the state, it is a trend for environmental protection to promote coal-fired emissions targets to be gradually drawn close to those of combustion engine based on ensuring low power cost and high thermal efficiency. However, in order to make the coal-fired units satisfy requirements of ultra-clean emissions targets, the main difficulty is to control the emission of fine particles in fly ash. At present, the diameter of the fine particles emitted from the outlet of electrostatic precipitator (ESP) in coal-fired power plant is ranged in 0.1-3 μm, wherein fine particles such as glass microsphere with diameter less than 2.5 μm account for more than 90% of the total escape particles. It is due to the factors of boiler type, combustion method, boiler temperature, and chemical composition of the coal. Referring to the cenosphere emitted from the coal-fired boiler electrostatic precipitator, the mass concentration of the cenosphere is ranged in 3-30 mg/m3, the composition is mainly SiO2 and Al2O3, and the cenosphere is characterized in fine particles, smooth and hydrophobic surface, high electrical insulation, flame retardant, temperature resistance and thermal insulation, and so on. However, due to the high specific resistance of the cenosphere (100-120° C., the specific resistance is 5×1011-1012Ω·cm) and its low charge performance, the efficiency of conventional electrostatic precipitation technology is limited in removal of cenosphere. In other words, for the coal-fired boiler utilizing fine ground coal powder and low nitrogen method, it is almost impossible to reach the emissions target of coal-fired ash <4.5 mg/m3 by conventional ash removal technical approach only due to the contribution of microsphere itself. Therefore, deep emission control of fly ash microsphere in coal-fired power plant is the key to make the coal-fired units satisfy the emissions targets of combustion engine.
According to related researches, with surface metallization or chemical coating, the coal-fired microsphere can be used in the field of aviation, aerospace, building material, vehicle, weaponry and so on. Surface modified microsphere takes the advantages of low density, high conductivity and so on. Moreover, in some super-hydrophobic surface (such as polydimethylsiloxane (PDMS), silicon wafer, glass etc.) under the condition of condensation, the difference of uniformity that the condensate is permeated into the surface will directly affect the degree of modification on hydrophobicity and uniformity. In this sense, for the microsphere with low removal efficiency caused by low charge performance, if appropriate surface condensation process is adopted, the specific resistance of the microsphere will be decreased in the order of magnitude, which is benefit to be charged and collected under the existence of electrostatic field, and thus is significant to realize ultra-clean emission of coal-fired ash.